1. Field of the Invention
The present invention relates to a brush holder support in a dynamic electric machine such as an electric motor.
2. Description of the Related Art
In general, a dynamic electric machine of the kind mentioned above incorporates brushes which are resiliently pressed onto commutator rings. There is a trend for a greater number of poles in this type of machine, in order to improve performance.
In such a dynamic electric machine having a large number of poles, it is necessary that a plurality of brushes 3 are arranged at a small pitch as shown in FIGS. 5 and 6. The electrical connections between the connecting portions 8 of the brushes 3 of the same polarity are achieved through soldering of lead lines and jumper lines 9a, 9b, or by spot-welding pig-tails 4 of the brushes directly to end portions of the brush holders. Such spot-welding is not easy to conduct because it is quite difficult to insert a welding electrode to the restricted regions where the brushes are densely arranged. In addition, there is a risk that the brush holder 2 will be undesirably deformed due to interference between the electrode and the brush holder 2.
The pig-tail 4 is required to have a certain length in order to enable the brush 3 to be mounted in the brush holder 2 and also to maintain electrical connection to the brush 3 even when the brush 3 has been worn down. Therefore, the pig-tail 4 connected to a brush may undesirably interfere with the brush spring which urges another brush 3, thus causing an electrical short-circuit. This problem would be avoided by ensuring electrical insulation between the springs and the pig-tails 4. Such a measure, however, inevitably leads to an increase in the size of the brush holder and, hence, of the dynamic electric machine.